Re-Roofing? Converting Low Slope Shingles to Flat Roof Membrane Roofing on Your Home or Considering Converting a Flat Roof to a Pitched Roof?
General Roofing Systems Canada Re-roofs Low Slope Roofs throughout Canada. Our roofing services are available in Toronto, Calgary, Red Deer, Edmonton, Lloydminster, Saskatoon, Regina, Medicine Hat, Lethbridge, Canmore, Kelowna, Vancouver, Whistler and points between.
Below you will find comments regarding various aspects of roofing conversions from our senior project manager.
One common challenge homeowners have when considering re-roofing a flat roof or a low slope roof on their home (we receive many inquiries about) are homes with a low slope pitch that currently have shingles on the roof and the homeowner is considering a conversion to a flat roof membrane when they re-roof instead of the shingles. Or, homeowners are considering converting a flat roof on their home to a pitched or sloped roof instead.
Low Slope Roofing Challenges
Low slope roofs on residential homes (in colder climates like most of Canada) can pose a significant challenge.
Vaulted Ceilings: Often these homes have vaulted or cathedral ceilings. The vault in the ceiling replaces the traditional steep pitch home attic space. The issue with this home design is that hot air from the inside of the house can more easily get to the underside of the roof sheathing. The problem with this is that the warm air causes snow on the roof to melt. Then when it cools down at night the melting snow turns in to ice and over time ice dams develop on the roof.
Attic / Roof Space Insulation: In these homes it is often the case that the insulation value is poor. Either as a result of moisture (roof leaks or condensation) or in many instances when the home was built very little insulation was placed in the roof cavity. Lack of insulation allows the hot air from in your home to get to the underside of the roof causing ice dams. It is critical to have proper insulation R values in your roof.
Ice Dams: The problem with ice dams is that they wreck roof membranes and roof shingles and cause leaks into your home. So basically what occurs is that the heat from in your home gets in to the roof assembly (sometimes the vapor barrier is non existent or faulty), gets past the vapor barrier, through a lack of insulation and heats the underside of the sheathing and ice dams build up. A steep slope roof has more opportunity to vent the hot air out of the attic because of the larger space available in the attic, the intake cold air at the soffits and the exhaust vents at the ridge (and the pitch is steep and taller which helps). Ice dams will work their way up the roof slope as freeze thaw continues. As the ice dams work their way up the slope the ice dams push up shingles and get under the shingles and melt as a result of the hot air from your home entering the roof cavity and this causes leaks in to the home. Low slope membranes are not as susceptible to this problem because the membrane systems are harder for ice to get under. If you stay with shingles vs. a low slope membrane you can also use Ice & Water membrane under shingles. A good drip edge at the eave edge may also help.
Ice & Water Membrane (for under shingles): Ice & Water membrane is a self-adhered membrane that should be installed in warm weather (commonly referred to as a peel and stick). With a low slope roof like a 3:12 you can get away with using Ice & Water on the whole roof and installing shingles over top. “Get away with” is a loose term I suppose – it isn’t guaranteed that just this step will solve your condensation or roof leak issues from ice damming. Your roof assembly and / or attic system is like the lung of your home. Just solving one of the many potential problems (such as installing Ice & Water) may or may not solve the problem. If your roof is a steeper pitch like 5:12 or more then I would only recommend Ice & Water at the eave area (about 44″), in valleys (under valley metal), and around penetrations etc. Our main website has a lot of information about these details at www.grscanadainc.com. Click on “steep slope roofing” and view the various article, links, etc.
Anyway, back to low slope roofing issues and Ice & Water membranes…
Ice & Water membrane is suggested because when the hot air from your home gets to the underside of the shingles and ice dams melt under your shingles the Ice & Water may keep the water from getting into your home. But it may not. At issue is that when one installs the shingles over the Ice & Water, the shingle nails are now penetrating the Ice & Water membrane. BE CAUTIOUS with claims by roofing salespeople that tell you this is not a problem because the Ice & Water or peel and stick will “self heal”. In other words, the claim is that when the nail penetrates the membrane that the membrane will seal around the nail – or self heal. Not all peel and stick membranes do this and you are relying on it actually occurring – there is no way to know if it did or did not seal around the nails because the shingles are now installed over top of the membrane.
Frost and Condensation: Frost will collect on the underside of your roof deck sheathing if hot air from your home gets to that area. When the frost melts it can appear as though you have a roof leak when water appears on the ceiling. Condensation can also make itself appear as a roof leak. As warm air enters the attic or roof assembly and has no where to go (your roof exhaust vents are not performing properly) then the condensation can turn in to leaks. This will typically manifest at walls, windows and doorways. Condensation can slowly ruin the complete structural components of any home. Leaks can be occurring over years inside walls and slowly destroying your home, not to mention the issues with mold and mildew.
Attic Ventilation: Attic ventilation is critical. Venting your attic or roof space (limited in vaulted or cathedral ceiling homes) is critical. If you do not get the warm air out of the attic or roof assembly in an efficient manner that heat will cause many problems (as above – ice dams, frost, and condensation that cause leaks).
Soffit: Also known as the cold air intake portion. The soffit area of your home is the breath in part of your roof assembly lung. The soffits are located under the roof overhang. Sometimes they are located at the wall or vertical part of the exterior of your home. This scenario (soffits at the wall) is common in “architecturally designed” homes that are looking for a certain street appeal. Anyway, intake soffits are critical. The cold air must enter the roof assembly and travel along the underside of the sheathing and in the process take the warm air from your home (that is entering the attic) out and be exhausted by way of a rooftop vent, whirlybird or ridge vent system.
Be sure the soffit intake air is not being hindered by attic insulation. Very often home owners that do not understand the principals of attic ventilation that do their own home renovations will put insulation over the intake vents of soffits. Be sure there is no insulation over the vent areas around the edges of your attic space.
Roof Vents: The exhaust portion of your attic or roof assembly. Roof exhaust ventilation is critical. Their are various guides for how much roof ventilation a home needs, but the problem with these guidelines is that every roof system and attic or roof assembly is different. The common guide is that for every 100 – 300 square feet of attic space you should have at least one square foot of rooftop ventilation (exhaust). We can help you design a roof vent exhaust plan to bring your probability of success as high as possible.
One quick side note about roof vents… I very often am witness to home-owners that get so frustrated trying to solve ice dam, ventilation, leaks, condensation and the like (especially with low slope roofs) that they end up listening to any snake oil or uneducated roofing salesman or roofer. And what occurs is that they end up with a combination of roof vents on their roof. DO NOT allow just anyone to start adding roof vents. A whirly bird installed near static vents on a roof will not work. It will cause the air to get sucked in to the roof attic and run immediately to the other vent and out – which does not help the cause to say the least.
Vapor Barrier: And finally we get to the vapor barrier. The problem with the vapor barrier is that finding gaps or holes in a vapor barrier can take time. Look for any penetrations through the vapor barrier. Inspect these areas closely. You may want to re-tape or caulk or seal in some way all penetration just to be sure they are air tight. If you have a low slope roof assembly this is near impossible because you can’t crawl in to the roof space typically.
Is there good news? I feel bad for homeowners that have these problems – they put their life savings into a home that in some cases becomes such an aggravation that much of their life can become consumed with the problem because in some instances the problem is literally destroying their home, the family peace, and their life long investment.
There is good news, but often it takes a lot of patience with the person or company that is helping you and it often takes significant investment.
My advice is to be sure you have an expert. An expert can take you through a logical process of elimination. In other words, the possible reasons for the problem are such… and the list is in order of priority… and at each step of remediation lets take a look at how the roof assembly now performs under different weather and seasons.
Our experts are often booked months in advance and I know that anyone else that I’ve met that is an expert at this is also booked well in advance normally. Don’t let that discourage you, book with an expert and take the time it takes to get it done right and save your investment money and peace of mind. And be very careful with quick fix salespeople in this category of work because you could be throwing good money after bad if you choose the wrong company or so-called expert.
Call or write us anytime… in this instance I would recommend you write us and email your situation to email@example.com. The issue with just a phone call to our call center is that you will be put on a waiting list that could be for many months. But a letter can be tackled sometimes remotely by staff that have some extra time while in the office. Be sure to include when you purchased your home, the issues you are facing with your attic or roof, if the leaks or condensation issues are occurring only when it melts on a nice winter day or if issues are present when it is bitter cold in winter or even in summer. It really helps to get photos of your home from street view and rooftop view because we can often suggest solutions even before we attend for a rooftop and attic inspection.
Some considerations for low slope re-roof planning for your home:
Low Slope Roof Membranes
Today there are many more options than once available for home-owners considering flat roof or low slope roofing membranes for re-roofing. We can remove the shingles on your home and apply a number of different systems.
Homeowners call us with concerns over the cost of low slope or flat roof membranes (relative to shingles) and this becomes a serious consideration when planning for a residential re-roof project.
Low slope roofing has changed and many options are now available for re-roofing your home that are much less costly than the traditional low slope tar roofing or torch down roll roofing.
The other thing that home-owners often call about is taking a low slope or a flat roof and having it turned in to a pitched (or a high slope) roof.
Today, solutions are available for low slope residential roofs that don’t require the cost of traditional flat roofing or the expense to go from a flat roof to a pitched slope roof on a home.
Newer low slope roofing membranes are “single ply”. EPDM is a single ply low slope roofing membrane that has a 10 – 30 year membrane warranty (the membrane warranty is available for residential re-roofing as well as commercial re-roofing) and some flat roofers will tell you they expect the newer single ply roofing membranes to last 30 or 40 years. TPO is also a single ply low slope white roofing membrane. Also available is PVC – PVC is similar to TPO in that it is single ply and typically installed as white.
There are the older style systems being the torch down sbs modified bitumen roofing membrane (or roll roofing) and Tar and Gravel flat roofing (or BUR / built-up roofing).
All membrane systems listed above work on low slope re-roofing projects.
And finally, there are metal roof or steel roofing systems for low slope re-roofing and even shingles for slopes to about a 4/12 pitch. Some roofing contractors are applying low slope shingles to 3/12 but we consider it a tentative practice at 3:12.
Low Slope Residential Re-Roofing
EPDM Membrane: The residential low slope roof in the pictures of this post are of a residential low slope roof that we are re-roofing this week. The low slope shingles are being torn off and replaced or re-roofed and converted to an EPDM flat roof membrane. The EPDM roofing membrane system carries a 20 year manufacturer warranty.
Attic Insulation: Also in the re-roofing process, we are removing the sheathing from this home and an attic insulator is blowing in insulation. We are then re-sheeting the roof deck substrate and adding a low slope insulation board and finishing the roof assembly with EPDM low slope roofing.
Flashing: All the roof flashings are being replaced in the re-roofing process – the eave, gable, chimney etc will be replaced as will all roof penetrations. The two low slope skylights are being replaced.
Ventilation: The venting of this low slope re-roofing project will be redesigned and installed at the ridge or peak of the roof with a custom made ridge ventilation system that will have a curb framed in first and then the ridge vent along the ridge. This will allow for proper attic / roof space airflow and ventilation, it will keep snow from covering the ridge vent, as well the custom framed curb for the vent will keep snow from entering the roof system.
You can follow this residential re-roof project by checking back regularly on our roofing blog as we will post pictures showing the process of re-roofing from a low slope shingle roof to a low slope flat roofing membrane.
Until next time,
The Roofers at GRS
General Roofing Systems Canada (GRS)
24 Hour Emergency Roof Repair: Call +1.877.497.3528 toll-free.
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